Pepsi Free
From Futurepedia, the Back to the Future Wiki
Pepsi Free was a caffeine-free Pepsi cola which was popular in 1985. When Marty McFly ordered a Pepsi Free in 1955 in Lou's Cafe, the cafe owner thought Marty was asking for a free Pepsi. Pepsi Free is later renamed Caffeine Free Pepsi in 1987 and is not referenced again most likely due to this.
